This disclosure relates to systems and methods for atomic layer deposition (ALD) of thin films on a surface of a substrate using radical species.
An overview of conventional ALD processes is provided in Atomic Layer Epitaxy (T. Suntola and M. Simpson, eds., Blackie and Son Ltd., Glasgow, 1990), which is incorporated herein by reference. Numerous patents and publications describe the use of radicals in connection with thin film deposition techniques, including atomic layer deposition (ALD) and sequential chemical vapor deposition. Many chemistries for radical-enhanced ALD (REALD) have been proposed, and many more are expected to be developed in view of the need for efficient production of high quality thin films in semiconductor manufacturing and other industries. Of particular interest are methods of forming non-semiconductor films, such as pure metal films, for use in integrated circuits and for other purposes. See, e.g., U.S. Pat. No. 6,616,986 B2 of Sherman and U.S. Pat. No. 6,200,893 B1 of Sneh.
Radicals (also sometimes called “free radicals”) are unstable atomic or molecular species having an unpaired electron. For example, hydrogen gas exists principally in diatomic molecular form, but molecular hydrogen may be split into atomic hydrogen radicals each having an unpaired electron. Many other radical species are known. In embodiments described herein, the radicals produced and used in the thin film deposition process may include highly-reactive radical gas species formed of a single element such as hydrogen, nitrogen, oxygen (e.g. ozone), or chlorine, as well as compound radicals such as hydroxide (OH).
U.S. Provisional Patent Application No. 60/743,786, filed Mar. 26, 2006 (“the '786 application”), and related U.S. patent application Ser. No. 11/691,421, filed Mar. 26, 2007 (“the '421 application”), both titled “Atomic Layer Deposition System and Method for Coating Flexible Substrates, are incorporated herein by reference. The '786 and '421 applications describe systems and methods for ALD in which a substrate such as a flexible web is moved through two or more precursor chambers or zones separated by an isolation chamber or zone to accomplish atomic layer deposition of thin films on the surface of the substrate. As the substrate traverses between the precursor zones, it passes through a series of flow-restricting passageways of an isolation zone into which an inert gas is injected to inhibit migration of precursor gases out of the precursor zones. In the technique described in the '786 and '421 applications, only the substrate gets coated and not the reaction chamber walls or other parts of the system. The present inventors have recognized that the processing system and method of the '786 and '421 applications enables the use of UV light or steady-state plasmas in one or more chambers to generate precursor radicals, instead of requiring radicals to be cyclically introduced into and removed from a common reaction chamber, as has previously been proposed by Sherman, Sneh, and others.
The present inventors have also recognized that oscillating, reciprocating, or circular movement of a substrate can be employed to accomplish ALD processes using precursor radicals that are continuously introduced into a reaction space by a steady-state radical source. When the systems and methods described herein are applied to accomplish thin film deposition processes with radicals, there may be unique benefits and capabilities that are enabled.
Further aspects of various embodiments will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings.